JP4716508B2 - X-ray tube - Google Patents

Description

  The present invention relates to an X-ray tube in which an electron beam is irradiated from a dedicated cathode to a plurality of regions on the counter cathode.

An X-ray tube is known in which an electron beam is irradiated from a dedicated cathode to a plurality of regions on the counter cathode (Patent Document 1 and Patent Document 2).
JP-A-1-161645 JP-A-6-215710

  The X-ray tube disclosed in Patent Document 1 includes a molybdenum target and a rhodium target on a rotating counter cathode. The molybdenum target is irradiated with the electron beam emitted from the first filament, and the rhodium target is irradiated with the electron beam emitted from the second filament. The first filament and the second filament are attached to the cathode and fixed in the X-ray tube. Then, X-rays can be generated from either one of the targets by applying a filament heating voltage to either the first filament or the second filament. As a result, any one of two types of characteristic X-rays having different wavelengths can be generated. Similarly, Patent Document 2 irradiates two types of targets, copper and chromium, on a rotating counter cathode with electron beams from dedicated filaments.

There is also known an X-ray tube including a plurality of cathodes, wherein the cathodes are switched by moving these cathodes in the X-ray tube (Patent Document 3).
Japanese Patent Laid-Open No. 4-188552

  The X-ray tube disclosed in Patent Document 3 includes a plurality of cathodes for forming different focal dimensions, and these cathodes are arranged on a circular base plate and the base plate is rotated. Thus, the cathode that emits the electron beam can be switched. Regardless of which cathode is selected, the electron beam emitted from the cathode irradiates almost the same region on the counter cathode. Thus, although a plurality of cathodes are disclosed, a plurality of regions on the counter cathode are not disclosed.

  When the technique disclosed in Patent Document 1 or Patent Document 2 is used, an electron beam can be irradiated from a separate cathode to a plurality of targets made of different materials, and the X-ray wavelength can be switched. By the way, considering an actual electron gun, the cathode is arranged inside the opening of the Wehnelt electrode. Assuming that a Wehnelt electrode is provided for each cathode, in order to arrange a plurality of cathodes side by side, it is necessary to increase the distance between the centers of the cathodes by at least the dimension of the Wehnelt electrode (for example, several tens of mm is required ). On the other hand, for example, considering that a plurality of target materials are arranged side by side on the rotating counter cathode, it is not preferable to increase the distance between the centers of the plurality of target materials. When the distance between the centers of a plurality of target materials is increased, the position of the X-ray focal point is greatly changed by switching the target materials (that is, by switching the wavelength of the characteristic X-ray to be extracted). Further, when the distance between the centers of the plurality of target materials is increased, the size of the rotating counter cathode is increased, and as a result, the size of the X-ray tube is also increased. Therefore, considering an actual rotating counter-cathode X-ray tube, as disclosed in Patent Document 1 or Patent Document 2, a plurality of cathodes are fixedly arranged and a cathode heating voltage is applied only to a desired cathode. Adopting the technical means of, has the disadvantages described above.

  On the other hand, according to the technique disclosed in Patent Document 3, only the cathode to be used can be opposed to the electron beam irradiation region of the counter cathode by moving a plurality of cathodes. However, in Patent Document 3, even if the cathode to be used is changed, the position of the electron beam irradiation region on the counter cathode is almost the same. Therefore, even if this technique is adopted, it is impossible to irradiate an electron beam from a separate cathode to each of the counter cathodes having a plurality of target materials.

  An object of the present invention is to easily switch the wavelength and focal size of an X-ray in an X-ray tube in which an electron beam is irradiated from a separate cathode to a plurality of regions on the counter-cathode, It is another object of the present invention to provide an X-ray tube in which the distance between the centers of the plurality of regions described above can be reduced and the size of the X-ray tube does not become so large.

  The present invention relates to an X-ray tube in which an electron beam is irradiated from a separate cathode to a plurality of regions on the counter cathode, and has the following features. First, the X-ray tube has an anti-cathode and an electron gun assembly, and the anti-cathode has a first region and a second region. The electron gun assembly includes a first electron gun including a first cathode that emits a first electron beam that collides with the first region, and a second cathode that emits a second electron beam that collides with the second region. And a second electron gun. The following features (a) to (c) are provided. (A) The first electron beam and the second electron beam are substantially in one plane. (A) The electron gun assembly is rotatable around a rotation center line perpendicular to the plane. (C) The electron gun assembly rotates around the rotation center line so that the first cathode faces the first region, and the second cathode faces the second region. The posture can be switched between the second posture.

  In the present invention, “substantially in one plane” has the following meaning. The cross section of the first electron beam and the cross section of the second electron beam have a predetermined thickness in the direction of the rotation center line of the electron gun assembly. In this case, the first electron beam in the direction of the rotation center line of the electron gun assembly is used. The center position of the electron beam thickness and the center position of the second electron beam thickness are in one plane (in a common plane). Of course, not all of the cross section of the first electron beam and all of the cross section of the second electron beam need be in one plane.

  The first electron gun and the second electron gun are each provided with a terminal for supplying a heating voltage to each cathode. That is, the first electron gun has a pair of first terminals connected to the first cathode, and the second electron gun has a pair of second terminals connected to the second cathode. On the other hand, the X-ray tube has a pair of cathode power supply terminals. When the electron gun assembly is in the first position, the first terminal is connected to the cathode power supply terminal and the electron gun assembly is in the second position. The second terminal is connected to the cathode power supply terminal.

  In order to switch the cathode that emits the electron beam, the following configuration can be adopted. The electron gun assembly can be switched from the first position to the second position by rotating 180 degrees around the rotation center line, or can be switched from the second position to the first position. In this case, an eccentric structure can be employed in which the cathode center line passing through the center of the first cathode and the center of the second cathode is separated from the rotation center line of the electron gun assembly by a predetermined distance. Thus, the position of the first electron beam and the position of the second electron beam can be made different from each other only by rotating the electron gun assembly 180 degrees.

  The material of the first region and the material of the second region can be different from each other. As a result, two types of wavelengths of X-rays can be switched and extracted. Separately from this, the focal size of the first electron beam on the first region and the focal size of the second electron beam on the second region can be made different from each other. In addition, different materials and different focal dimensions can be combined. Furthermore, three or more regions may be provided on the counter-cathode, and three or more electron guns may be provided correspondingly.

  The counter-cathode may be a fixed counter-cathode (stationary counter-cathode) or a rotating counter-cathode. In the case of the rotating anti-cathode, the first region and the second region can be arranged next to each other in a direction parallel to the rotation center line of the rotating anti-cathode.

  According to the present invention, in an X-ray tube in which an electron beam is irradiated from a separate cathode to a plurality of regions on the counter cathode, the arrangement structure of two electron guns is devised, so that Wavelengths and focal dimensions can be easily switched, the distance between the centers of a plurality of regions on the counter cathode can be reduced, and the size of the X-ray tube need not be so large.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a perspective view of an essential part of an embodiment of an X-ray tube according to the present invention. The X-ray tube includes a rotating counter cathode 10 and an electron gun assembly 12. The rotating anti-cathode 10 has a cylindrical shape and rotates around the rotation center line 14. The rotation center line 14 extends in the horizontal direction. A first region 16 and a second region 18 are formed on the outer peripheral surface of the rotating counter cathode 10. The first region 16 and the second region 18 are band-like regions extending in the circumferential direction, and are adjacent to each other in a direction parallel to the rotation center line 14. The material of the first region 16 is Cr (chromium), and the material of the second region 18 is Cu (copper). The widths of the first region 16 and the second region 18 are each about 4 mm. The diameter of the rotating counter cathode 10 is 280 mm.

  The electron gun assembly 12 includes a turntable 20, a first electron gun 22, and a second electron gun 24. The turntable 20 can rotate around the rotation center line 25. The rotation center line 25 extends in the vertical direction. The first electron gun 22 and the second electron gun 24 are fixed to the turntable 20. The first electron gun 22 includes a first Wehnelt electrode 26 and a first cathode 28. A first cathode 28 is disposed inside the opening 30 of the first Wehnelt electrode 26. The first cathode 28 is a coiled filament. The first cathode 28 is connected to a pair of first terminals 29. The first terminal 29 is exposed above the first electron gun 22.

  The second electron gun 24 has the same structure as the first electron gun 22, and includes a second Wehnelt electrode 32 and a second cathode 34. A second cathode 34 is disposed inside the opening 36 of the second Wehnelt electrode 32. The second electrode 34 is also a coiled filament. The second cathode 34 is connected to a pair of second terminals 35. The second terminal 35 is exposed above the second electron gun 24.

  In FIG. 1, the electron gun assembly 12 is in a neutral position, and none of the cathodes faces the rotating counter cathode 10. In this neutral position, no heating voltage is applied to any cathode.

  FIG. 2 is a perspective view of the main part of the X-ray tube when the electron gun assembly 12 is in the first posture. When the electron gun assembly 12 in the neutral position in FIG. 1 is rotated 90 degrees counterclockwise as viewed from above, the first position in FIG. 2 is obtained. At this time, the first electron gun 22 faces the rotating counter cathode 10 and the first cathode 28 faces the first region 16 of the rotating counter cathode 10. As will be described later, the first terminal 29 is connected to the cathode power supply terminal. The first electron beam 38 emitted from the first cathode 28 collides with the first region 16, and Cr characteristic X-rays are generated from the electron beam irradiation region (X-ray focal point).

  FIG. 3 is a perspective view of the main part of the X-ray tube when the electron gun assembly 12 is in the second posture. When the electron gun assembly 12 in the neutral posture of FIG. 1 is rotated 90 degrees clockwise as viewed from above, the second posture of FIG. 3 is obtained. Alternatively, when the first posture shown in FIG. 2 is rotated 180 degrees counterclockwise as viewed from above (or 180 degrees clockwise), the second posture shown in FIG. 3 is obtained. At this time, the second electron gun 24 faces the rotating counter cathode 10 and the second cathode 34 faces the second region 18 of the rotating counter cathode 10. The second terminal 35 is connected to the cathode power supply terminal as will be described later. The second electron beam 40 emitted from the second cathode 34 collides with the second region 18, and Cu characteristic X-rays are generated from the electron beam irradiation region (X-ray focal point).

  To switch from the first position of FIG. 2 to the second position of FIG. 3, it is only necessary to rotate the electron gun assembly without breaking the vacuum of the X-ray tube. Therefore, the operation of switching the wavelength of the X-ray extracted from the X-ray tube is very easy and takes a short time.

  FIG. 4 is a plan cross-sectional view of the main part of the X-ray tube when the electron gun assembly 12 is in a neutral position. A rotating counter cathode 10 is rotatably attached to an X-ray tube vacuum vessel 42 (tube shield). The rotating anti-cathode 10 rotates around the rotation center line 14. The vacuum vessel 42 is provided with two windows 44 and 46 made of beryllium. The electron gun assembly 12 can rotate about a rotation center line 25. The first electron gun 22 and the second electron gun 24 are arranged back to back with the rotation center line 25 in between. A straight line 48 (hereinafter referred to as “cathode center line”) passing through the center in the longitudinal direction of the first cathode 28 (the center in the left-right direction in FIG. 4) and the center in the longitudinal direction of the second cathode 34 is referred to as the rotation center line 25 And a predetermined distance D. In this example, D is 1.7 mm. As described above, the two electron guns 22 and 24 are arranged eccentrically with respect to the rotation center line 25 of the electron gun assembly 12. On the other hand, the distance L between the center in the width direction of the first region 16 and the center in the width direction of the second region 18 of the rotating cathode 10 is 3.4 mm, and D is set to be half of L. . In this way, the position of the first electron beam and the position of the second electron beam can be shifted by a predetermined distance (that is, by 3.4 mm) simply by rotating the electron gun assembly by 180 degrees. In this embodiment, it is assumed that the dimension of the electron beam irradiation area (that is, the focal dimension) is 0.07 mm × 0.7 mm. By the way, it is not always necessary to have the center of the electron beam at the center of the first region 16 in the width direction and the center of the second region 18 in the width direction, but within the range of the width of the first region 16 and the second region 18. It is sufficient that the electron beam is within the range of the width.

  The pair of first terminals 29 exposed at the top of the first electron gun 22 and the pair of second terminals 35 exposed at the top of the second electron gun 24 are point-symmetric about the rotation center line 25. It is arranged to be. Accordingly, when viewed from the first electron gun 22, the pair of first terminals 29 are disposed at a biased position, and when viewed from the second electron gun 24, the pair of second terminals 35 are disposed at a biased position. Yes.

  FIG. 5 is a cross-sectional view similar to FIG. 4 when the electron gun assembly 12 is in the first position. When the electron gun assembly 12 is rotated 90 degrees counterclockwise around the rotation center line 25 as viewed from above from the neutral posture shown in FIG. 4, the first posture shown in FIG. 5 is obtained. The pair of first terminals 29 is connected to a cathode power supply terminal, and a predetermined filament heating voltage is applied to both ends of the first cathode 28. A predetermined negative high voltage is applied to the first electrode 28 with respect to the rotating cathode 10. As a result, the first electron beam 38 is emitted from the first cathode 28 toward the first region 16 of the rotating counter cathode 10. Further, a predetermined voltage is applied between the first cathode 28 and the first Wehnelt electrode 26, and the first electron beam 38 is narrowed down to a desired focal size on the first region 16 of the rotating counter cathode 10. . From the electron beam irradiation region (X-ray focal point) on the first region 16, Cr characteristic X-rays 50 are generated. When the first rotation passage 45 in the vicinity of the first window 44 is opened, the Cr characteristic X-rays 50 exit from the first window 44.

  6 is a cross-sectional view similar to FIG. 4 when the electron gun assembly 12 is in the second position. When the electron gun assembly 12 is rotated 90 degrees clockwise around the rotation center line 25 as viewed from above from the neutral posture shown in FIG. 4, the second posture shown in FIG. 6 is obtained. Alternatively, when the electron gun assembly 12 is rotated 180 degrees counterclockwise or 180 degrees clockwise around the rotation center line 25 as viewed from above from the first position shown in FIG. Become two postures. The pair of second terminals 35 are connected to a cathode power supply terminal, and a predetermined filament heating voltage is applied to both ends of the second cathode 34. Further, a predetermined negative high voltage is applied to the second electrode 34 with respect to the rotating counter cathode 10. As a result, the second electron beam 40 is emitted from the second cathode 34 toward the second region 18 of the rotating counter cathode 10. Further, a predetermined voltage is applied between the second cathode 34 and the second Wehnelt electrode 32, and the second electron beam 40 is narrowed to a desired focal size on the second region 18 of the rotating counter cathode 10. . Cu characteristic X-rays 52 are generated from the electron beam irradiation region (X-ray focal point) on the second region 18. When the second rotation passage 47 in the vicinity of the second window 46 is opened. Cu characteristic X-rays 52 exit from the second window 46.

  The first electron beam 38 in FIG. 5 is in a horizontal plane including the rotation center line 14 of the rotating anti-cathode 10. This plane is called an electron beam plane. The electron beam plane is perpendicular to the rotation center line 25 of the electron gun assembly 12. Incidentally, the first electron beam 38 has a predetermined thickness in the direction of the rotation center line 25 of the electron gun assembly 12 (that is, in the vertical direction). Therefore, strictly speaking, the center position of the thickness in the vertical direction of the cross section of the first electron beam 38 is within the above-described electron beam plane. Similarly, the center position of the thickness of the second electron beam 40 in FIG. 6 is in the electron beam plane. Therefore, it can be said that the first electron beam 38 and the second electron beam 40 are substantially in one plane (in a common plane).

  5, the dimension (focal dimension) of the first electron beam 38 on the first region 16 of the rotating anti-cathode 10 and the dimension of the second electron beam 40 on the second region 18 of the rotating anti-cathode 10 in FIG. (Focal dimensions) may be the same or different from each other. In order to make the focal dimensions different from each other, the shapes and dimensions of the cathodes 28 and 34 are made different from each other, and the shapes and dimensions of the openings 30 and 36 of the Wehnelt electrodes 26 and 32 are also made suitable for the cathodes 28 and 34.

  FIG. 7 is a plan view of the electron gun assembly 12 in which the positions of the cathode power supply terminals 54 are shown superimposed. A pair of first terminals 29 are exposed on the upper surface of the first electron gun 22. A pair of second terminals 35 are exposed on the upper surface of the second electron gun 24. The first terminal 29 and the second terminal 35 are arranged point-symmetrically about the rotation center line 25 of the turntable 20. Further, the pair of first terminals 29, the pair of second terminals 34, and the pair of cathode power supply terminals 54 are placed on a circle 56 centered on the rotation center line of the turntable 20 as viewed from above. In FIG. 7, the electron gun assembly 12 is in a neutral posture, and neither the first terminal 29 nor the second terminal 35 is connected to the cathode power supply terminal 54.

  FIG. 8 is a plan view similar to FIG. 7 when the electron gun assembly 12 is in the first position. The pair of first terminals 29 of the first electron gun 22 are connected to the pair of cathode power supply terminals 54, respectively. The cathode power supply terminal 54 is stationary in the X-ray tube.

  FIG. 9 is a plan view similar to FIG. 7 when the electron gun assembly 12 is in the second position. A pair of second terminals 35 of the second electron gun 24 are connected to a pair of cathode power supply terminals 54, respectively.

  FIG. 10 is a side view of the main part of the X-ray tube shown in FIG. A cathode power supply mechanism 58 is disposed above the electron gun assembly 12. The cathode power supply mechanism 58 includes a pair of cathode power supply terminals 54 at the lower end thereof. By rotating the electron gun assembly 12 around the rotation center line 25, the cathode power supply terminal 54 is selectively connected to the first terminal 29 and the second terminal 35 as described above. In FIG. 10, the electron gun assembly 12 is in the first posture, and a filament heating voltage is applied to the first cathode 28 via the cathode power supply terminal 54 and the first terminal 29. The first electron beam 38 emitted from the first cathode 28 is irradiated to the first region on the rotating counter cathode 10. The first cathode 28 is disposed inside an opening 30 formed in the first Wehnelt electrode 26. Similarly, the second cathode 34 is also disposed inside the opening 36 formed in the second Wehnelt electrode 32.

  In the above-described embodiment, the combination of the material of the first region 16 and the second region 18 of the rotating counter cathode 10 is exemplified by a combination of Cu (copper) and Cr (chromium). However, the present invention is not limited to this. Alternatively, for example, a combination of Cu (copper) and Co (cobalt) or a combination of Cu (copper) and Mo (molybdenum) may be used.

  In the above-described embodiment, the first region 16 and the second region 18 of the rotating anti-cathode 10 are formed of different materials, but may be the same material. In that case, using the first electron gun 22 and the second electron gun 24, the focal dimension on the first region 16 and the focal dimension on the second region 18 are made different from each other, so that two types of X-rays with different focal dimensions are used. Can be switched out.

  Examples of combinations of different focal dimensions are: (1) a combination in which the first focal point is 0.07 × 0.7 mm and the second focal point is 0.15 × 1.5 mm. (2) A combination in which the first focus is 0.10 × 1.0 mm and the second focus is 0.15 × 1.5 mm, (3) the first focus is 0.10 × 1.0 mm, and the second Combination with a focal point of 0.30 × 3.0 mm, (4) Combination with a first focal point of 0.15 × 1.5 mm and a second focal point of 10.0 × 0.5 mm, (5) First focal point Is 0.10 × 1.0 mm and the second focus is 0.50 × 10.0 mm. (6) The first focus is 0.50 × 10.0 mm and the second focus is 10.0 × 0. A combination of 5 mm is conceivable. Among these, the combination of (1) to (4) assumes a rotating counter cathode having a diameter of 280 mm, and the combination of (5) and (6) assumes a rotating counter cathode having a diameter of 100 mm. .

It is a perspective view of the principal part of one Example of the X-ray tube which concerns on this invention. It is a perspective view of the principal part of an X-ray tube when an electron gun assembly exists in a 1st attitude | position. It is a perspective view of the principal part of an X-ray tube when an electron gun assembly exists in a 2nd attitude | position. It is a plane sectional view of the important section of an X-ray tube when an electron gun assembly is in a neutral posture. It is sectional drawing similar to FIG. 4 when an electron gun assembly exists in a 1st attitude | position. It is sectional drawing similar to FIG. 4 when an electron gun assembly exists in a 2nd attitude | position. It is a top view of an electron gun assembly, and shows the position of the cathode power supply terminal in an overlapping manner. FIG. 8 is a plan view similar to FIG. 7 when the electron gun assembly is in the first posture. FIG. 8 is a plan view similar to FIG. 7 when the electron gun assembly is in the second posture. It is a side view of the principal part of the X-ray tube shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Rotating anti-cathode 12 Electron gun assembly 14 Rotating anti-cathode rotating center line 16 1st area | region 18 2nd area | region 20 Rotating base 22 1st electron gun 24 2nd electron gun 25 Rotating stage rotating center line 26 1st Wehnelt electrode 28 First cathode 29 First terminal 30 First Wehnelt electrode opening 32 Second Wehnelt electrode 34 Second cathode 35 Second terminal 36 Second Wehnelt electrode opening 38 First electron beam 40 Second electron beam 42 Vacuum container 44 First 1 window 45 rotation passage 46 second window 47 second rotation passage 48 cathode center line 50 Cr characteristic X-ray 52 Cu characteristic X-ray 54 cathode power supply terminal 56 circle 58 cathode power supply mechanism

Claims (6)

A first electron gun having an anti-cathode having a first region and a second region, a first cathode that emits a first electron beam that collides with the first region, and a second electron beam that collides with the second region are emitted. An X-ray tube having an electron gun assembly having a second electron gun with a second cathode
(A) The first electron beam and the second electron beam are substantially in one plane,
(A) The electron gun assembly is rotatable around a rotation center line perpendicular to the plane,
(C) The electron gun assembly rotates around the rotation center line so that the first cathode faces the first region, and the second cathode faces the second region. The posture can be switched between the second posture and
An X-ray tube characterized by that.   2. The X-ray tube according to claim 1, wherein the first electron gun includes a pair of first terminals connected to the first cathode, and the second electron gun is a pair connected to the second cathode. The X-ray tube has a pair of cathode power terminals, and when the electron gun assembly is in the first position, the first terminals are connected to the cathode power terminals. The X-ray tube is characterized in that when the electron gun assembly is in the second position, the second terminal is connected to the cathode power supply terminal.   3. The X-ray tube according to claim 1, wherein the electron gun assembly rotates from the first posture to the second posture or the second posture by rotating 180 degrees around the rotation center line. 4. Switching from the posture to the first posture, and the cathode center line passing through the center of the first cathode and the center of the second cathode is separated from the rotation center line of the electron gun assembly by a predetermined distance. A featured X-ray tube.   The X-ray tube according to any one of claims 1 to 3, wherein the material of the first region and the material of the second region are different from each other.   5. The X-ray tube according to claim 1, wherein the counter-cathode is a rotating counter-cathode, and the first region and the second electrode are arranged in a direction parallel to a rotation center line of the rotating anti-cathode. An X-ray tube characterized in that the regions are arranged next to each other.   6. The X-ray tube according to claim 1, wherein a focal dimension of the first electron beam on the first region and a focal dimension of the second electron beam on the second region are set. An X-ray tube characterized by being different from each other.

Images